1. Field of Application
The present invention relates to a control system of an electrical generator of a vehicle, and in particular to an electrical generator control system whereby the production of voltage spikes in a supply voltage, resulting from disconnection of an electrical load, can be substantially suppressed.
2. Description of Prior Art
A motor vehicle is equipped with an electrical generator which is in general constituted as an alternator (e.g., 3-phase AC generator) that is driven by the vehicle engine, in combination with a rectifier circuit, to produce an unsmoothed DC output voltage. The electrical generator serves not only for charging the storage battery of the vehicle (referred to in the following simply as the battery) but also for supplying power to various types of electrical load. The level of output voltage of such an electrical generator, and hence the total value of output current that is supplied to the battery and the loads, is controlled through adjustment of the level of field current of the alternator, by varying the duty ratio of successive on/off switching of the field current. This control of the generator voltage is performed by a circuit generally referred to as the regulator.
Japanese patent publication No. 4-12639 describes such a prior art type of electrical generator control system, whereby when one of various electrical loads of that are supplied from the output of the electrical generator is disconnected, the magnitude of a resultant increase in the output voltage of the electrical generator is detected, and control is applied to lower that output voltage of and thereby reduce the level of generated current (by reducing the field current of the alternator) in accordance with the detected amount of voltage increase.
With such a prior art generator control method, a certain amount of delay will occur between the time point at which the electrical load is removed and the point at which control of generator output (reduction of the generated current level) becomes fully effective. Hence, a voltage spike that is of significant amplitude may occur at the time of load disconnection.
This is illustrated in FIG. 4, in which it is assumed that the level of current supplied by the electrical generator is reduced from 70 A to 40, when disconnection of a certain electrical load occurs at the time point t2. As shown, a voltage spike appears in the battery voltage (i.e., the output voltage of the electrical generator), and such voltage transients can have serious adverse effects upon the operation of various equipment of the vehicle, such as an ECU that performs overall control of the vehicle, equipment that controls the power steering system of the vehicle, etc.
In particular, if the level of current being supplied to the electrical load prior to its disconnection is high, and/or the battery is fully charged, or almost fully charged, then such a voltage spike will be large in amplitude.